Oil well production fluid refers to the composition obtained from earth formations such as geological reservoirs through oil wells. Such fluid normally consists of oil, natural gas and water. Typically it consists of at least 90% water and 10% or less of crude oil. Dissolved materials, such as the anionic salts of organic acids, are usually present in the water.
At surface level, the constituents of oil well production fluids are physically separated by such separation techniques as bulk separators and dissolved air flotation. In particular, the marketable constituents--gas and oil--are separated from the water. The separated water stream is referred to as "produced water". Produced water contains the above described water soluble organic materials. Conventional phase separation techniques will not remove such water soluble compounds from the aqueous phase.
Governmental regulations, in recognition of the need for conservation of the environment, prohibit the discharge of produced water into navigable waters without the removal first of the water soluble organics. In fact, under the Federal Water Pollution Control Act, as amended in 1972, it is unlawful to discharge any pollutant into a navigable water without first obtaining a permit under section 402 of the Control Act. 33 U.S.C.A. .sctn. 1311(a) (1977 Supp.).
After the produced water is separated from the oil and gas (of the oil well production fluid) it is necessary, assuming the produced water is to be discharged to surface waters, to measure the oil and grease content of the effluent produced water stream by gravimetric analysis. Oil and grease, which can include water soluble organic materials, must be reduced to 42 mg/l maximum and 29 mg/l monthly average for discharge to Outer Continental Shelf waters and, depending on EPA regional rules, must be reduced to 10-35 mg/l at onshore facilities.
Alternatively, in other areas where water is in short supply, such as in those areas adjacent to the Pacific coast, it is highly desirable to recycle the produced water for use on land. In order to make effective use of the water stream on land, it is necessary to decrease the oil and grease content of the aqueous effluent.
New methods are needed to readily and easily treat water soluble organic materials (WSOs) in produced water. One possibility is presented by the use of ozone--long considered to be a powerful oxidizing agent.
Extensively used in Europe as a bactericide, ozone recently has gained acceptance in the United States as a substitute for chlorine gas. Waste treatment facilities have also realized the advantages of using ozone for degradation of such natural organic matter as humic and fulvic acids. One of the main advantages of using ozone for the oxidation of hydrocarbons is its selectivity for forming nontoxic "oxygenated" products during partial oxidation. Furthermore, if needed, ozonolysis can be driven towards the total oxidation of those molecules forming carbon dioxide and water.
To date, no documentation exists addressing the successful use of ozonolysis with produced water. In large part this is due to the fact that ozone is relatively insoluble at the elevated temperatures in which produced water is conventionally processed. Thus, in order to make ozonolysis feasible it has long been considered necessary to first pretreat waters by cooling. In addition, pH adjustments, excessively long contact times and the use of such chemicals as hydrogen peroxide and, in some cases, UV lamps, have been considered to be mandatory. For most oil field applications these steps are not only uneconomical but also impractical.
The present invention provides a simple, economical procedure for accomplishing the stated objective. While known methods can reduce the content of water soluble organics to the desired low level, they are relatively complex and/or expensive in comparison with the process of the present invention.